1. Technical Field
The present invention relates generally to a laminating machine for applying protective coverings to relatively large items and in particular to improvements in laminating machine heating and cooling stations.
2. Description of the Prior Art
Known laminating machines are used to laminate protective coverings of relatively thin and narrow plastic material on relatively small paper or other core items, such as for driver's licenses and identification cards. Similarly, laminating machines are also used for laminating protective coverings over relatively larger items, such as menus and maps which often include an 81/2 inch by 11 inch, or larger, paper or cardboard core material supplied continuously or in individual sheets.
Prior machines for applying protective lamination to cores have typically, if not exclusively, had one of three types of heating arrangements to heat soften a bonding layer of the protective material. These are (i) stationary shoe heaters over which plastic strips are fed in sliding contact, such as shown in U.S. Pat. No. 3,413,171 to Hannon and entitled Process of Making Identification Cards, issued Nov. 26, 1968; (ii) spaced shoe heaters designed to transfer heat to a strip of film as it is fed around a feed roll, such as that shown in U.S. Pat. No. 3,143,454 to Harmon and entitled Laminating Press, issued Aug. 4, 1964; or, (iii) heater rolls around which a plastic web was fed. All of these have exhibited drawbacks. All were relatively inefficient limiting the throughput of a laminating machine to relatively low volumes. Usually, if not always, they lacked adequate controls to maintain consistent operational temperatures and an ability to quickly bring a machine to an equilibrium condition. As a consequence, control over such a machine to produce consistent and uniform finished product was accomplished by operator observation of products coming through the machine and adjusting the feed rate of the machine to produce uniform products.
These described drawbacks, while often attributable to relatively inefficient and relatively unstable film heating systems, were exacerbated by the failure to provide efficient cooling systems to cool laminations quickly and effectively to "freeze" the thermoplastic material functioning as a bonding agent to apply a protective covering to a core. When ambient conditions were hot so cooling was excessively slowed, an operator had to manually adjust the feed rate of the machine to slow it and lower the temperature of the heaters to appropriate levels for the slower feed rates.